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Any operation in which one solid is separated
from one another by floating one of them at or on
the surface of fluid (Brown, 1950)
Separation of mixed liberated particles in terms
of their wettability differences (Perry, 1997)
Based on the differences in the surface chemical
properties (i.e. wettability)
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One solid more readily adsorbs the water
phase, becomes surrounded by water, and
sinks
The other solid more readily adsorbs air and
becomes at least partially surrounded orcovered by air
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The average or bulk density
of the solid and adsorbed
air bubbles is less than thatof water
The whole mass of air and
solid floats to the surfaceto form a mineralized froth
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Prepare a water
suspension of a
mixture ofrelatively fine-sized particles
(smaller than 150micrometers)
Contact the
suspension with aswarm of airbubbles of air in asuitably designed
process vessel
Particles whichare readily wetted
by water - remain
in suspension
Particles that
are not
wetted by
water tendto attached to
air bubbles
The air bubbleslevitate (float) to
the top of the
process vessel
Collect in
a froth
layer
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Used in the mineral process industry to
concentrate mineral values (i.e. copper, lead,
zinc, molybdenum and nickel)
Used for the recovery of fine coal and for
the concentration of a wide range of mineralcommodities
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Wastewater treatment to remove particulate,
organic and biological contaminants
Extraction of metallic values
Removal of heavy metal compounds fromhydrometallurgical streams (precipitation
flotation)
Recovery of bitumen from tar sands
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Deinking of wastepaper
Recovery of solids from white waste inpaper making
Recovery of glass sands from industrial
wastes
Removal of impurities from peas
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Removal of ergot from rye
Separation of proteins from milk
Clarification of fruit juice
Extraction of soluble species (ion
flotation and foam fractionation)
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Rougher
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The first step Conditioning
The slurryor thepulp,consisting of particles to beseparated is fed in the
conditioning to which thenecessary flotationreagents are added
Particles are finely divided
material reduced by theball mill or other finecrusher, usually varying insize from 20 mesh to under200 mesh
Rougher
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The first step Conditioning
Purpose:
to create physical-
chemical conditions for
achieving appropriateselectivity between
particle species that are
to be separated
To cause complete
filming of the solid by
the reagent
Rougher
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The first step Flotation Reagent
Can be collectors,
frothers, and
modifiers
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Collectors
- surface-active agents that are added to the
flotation pulp, where they adsorb selectively on thesurface of the particles and render them
hydrophobic
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o Non-ionizing collectors
-practically insoluble in
water and cause theparticles to become
hydrophobic by covering
them with a thin film
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o Ionizing collectors
-dissociate into ions in waterare made up of complexheteropolar molecules in that the
molecule contains both a nonpolarhydrocarbon group withpronounced hydrophobicproperties and a polar group withhydrophilic properties
Anionic collectorsCationic collectors
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CollectorsDosage requirements depend on the mechanisms by which they interact with the
particle surface just to form monomolecular layer
RULE:High dosages are required for non-ionizing collectors and
physisorbing ionizing collectors (in the order of 0.1 to 1 g of reagent
per kg of solids)
Low dosages for chemisorbing ionizing collectors (0.01 to 0.1 g of
reagent per kg of solid)
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CollectorsDosage requirements depend on the mechanisms by which they interact with the
particle surface just to form monomolecular layer
NOTE:
Addition of excess quantities of a collector is not desirable because it
results in reducing the selectivity and increasing the cost
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Frothers
-surface-active agents added to the flotation pulp
primarily to stabilize the air bubbles for effective particle-bubble attachment, carryover of particle-laden bubbles to
the froth, and removal of the froth
-similar to ionizing collectors except that theyconcentrate primarily at the air-liquid interface
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Frothers
-i.e. pine oil, cresylic acid, polypropylene glycol, short-
chain alcohols and 5- to 8-carbon aliphatic alcohols
Dosage requirements are usually 0.01 to 0.1 g per kg of
solids
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ModifiersActivators- used to make a mineral surface
amenable to collector coating
pH regulators- used to control or adjust pH, a verycritical factor in many flotation separations
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ModifiersDepressants- assists in selectivity (sharpness of
separation) or stop unwanted minerals from
floating
Dispersants and flocculants- control slimes thatsometimes interfere with the selectivity and
increase reagent consumption
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ModifiersDosage requirement: Vary widely, ranging from as little as
0.01 to 0.1 g/kg to as high as 1 to 2 g/kg of solids,
depending upon the reagent and the metallurgical
problem
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Important phenomena that occur;
Solubility and dissociation of reagents in water
Change of pH of the suspension
Change of air-water surface tension
Physical and chemical adsorption of the dissolved species onthe solid surfaces due to hydrogen bond formation
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Important phenomena that occur;
Electrostatic interactions
Hydrophobic bonding
Chemical bond formation
Fixation of reagent species in the solid lattice
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o Involves relative interaction of three phases:solid, water and air
o Objective: To contact solid particlessuspended in water with air bubbles andcause a stable bubble-particle attachment
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Recall: Flotation depends upon the relativeadsorption or wetting of the solid surfacesby the fluid
This is controlled by surface or interfacialenergy
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Generally, The sum of the components of the interfacial
tensions equals to zero.
SG
SL
Gas
Solid
Liquid
Figure 96. Diagram of surface tensions involved in thee-phase contact.
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SG = SL + LG (cos )
where = interfacial tension of the solid-gas
(SG), solid-liquid (SL) and liquid-gas(LG),respectively
= contact angle
SG SL
Gas
Solid
Liquid
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When a solid particle attaches itself to abubble, there is a loss in surface energy Eper unit area of surface , equal to the loss inthe surface tension
E = -(SG SG + SL SL + LG LG)
E = SG SG + SL SL + LG LG
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Since,
SG
= SL
+ LG
(cos )
SL - SG = -LG (cos )
)( SG-LGSLSG
E
)( cos-1LGSG
E
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The second step Separation
Purpose:
To generate and
introduce air bubblesinto the process into the
process vesselRougher
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The second step Separation
Purpose:
Particles attached the air
bubbles are in mostapplication removed from
the process vessel
(flotation cell) as froth
Rougher
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Electrolytic or Electroflotation
Units Illustration
- based on the generation
of hydrogen and oxygenbubbles in a dilute aqueous
solution
- passes direct current
between two electrodes
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Electrolytic orElectroflotation Units Illustration
Choice of Electrode Materials
- aluminum- platinized titanium
- titanium coated
with lead dioxide- stainless steel
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Advantage- Bubble size tends to be the smallest(10 50 micrometer
-Very little turbulence
- attractive for the separation of small
particles and fragile flocs
-attractive for small installations in the
flowrate range of 10 20 cu.m/h
Electrolytic or
Electroflotation Units
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Disadvantage
- fouling of electrodes
- not suitable for potable watertreatment due to heavy metalcontamination
Electrolytic or
Electroflotation Units
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Application
- effluent treatment
and sludge thickening
Electrolytic or
Electroflotation Units
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Dissolved-air Flotation Unit Dissolved-air Flotation Unit
Saturation of processed stream
with air and generation of airbubbles by releasing pressure
Used to treat process streams
with low solid concentration
(0.01- 2% by vol)
No addition of frother-type
chemical reagents
Particle bubble contact
- achieved by direct
nucleation and growth of air
bubbles on the particles
Bubble size- range from 20
100 micrometers
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Dissolved-air Flotation Unit
Applications
- for sewage and water treatment of potable water
- treatment of slaughterhouse, poultry processing,
seafood processing, soap, and food processingwastes
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Two Main Types of Dissolved-air Flotation
Unit
1.Vacuum flotation
2.Pressure flotation
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Vacuum Flotation Unit
Saturation of process
stream with air at
atmospheric pressure and
introduction to the flotation
tank on which vacuum is
applied
Can be run only as a batch
process
Uses sophisticated
equipment to produce and
maintain vacuum
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Pressure flotation unit
Consists of pressurizingand aerating the process
stream and introducing it
into the flotation vessel
that is maintained atatmospheric pressure
Can be operated on a
continuous basis
Reduction of pressure-results in formation of fine
air bubbles
Pressurization can becarried out through full-
flow or split-flow pressure
flotation.
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Pressure flotation unit
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Dispersed-air Flotation Unit Generation of air bubbles by:
a. pneumatic
b. mechanical
Relatively large air bubbles (at least 1 mm in size)
Frothers are added to control the size and stability of air
bubbles
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- the equipment in which
the material is actually
separated or floated from theresidual tailings
- consists of a vessel provided
with a feed at one end, an
overflow for froth removal, anda discharge for tailing at the
opposite end
Flotation Cell
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Pneumatic Cells Mechanical Cell
- depend upon compressed air
for agitation
- relatively mild agitation
- produce a clean frothrelatively free from gangue
- more violent agitation, more
thorough flotation and tailingsmore nearly free from material
desired in the concentrate
- greater capacity for the same
volume
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Pneumatic Cells Mechanical Cell
- 50% longer contact time and
full conditioning of the pulpbefore flotation
- flotation columns
air-bubble generation is
accomplished by a gas-sparging system
- incorporate a mechanical
agitator that draws in air andbeats it into the pulp
- mechanical agitation and
aeration by means of a rotation
impeller on an upright shaft
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It is desired to recover lead from an orecontaining 10 percent lead sulfide (PbS) andthe balance assumed to be silica, 500 tons ofore being treated per 24-hr day.
It is assumed that the concentrate from asingle cell is of acceptable purity but thetailings are to be retreated in scavenger cellswith return of scavenger concentrate to therougher.
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Laboratory findings indicate that if water-to-solids ratio L/S =2 and the contact time is 8 min in the rougher and L/s = 4 for15 min in scavenger, with mechanically agitated machines ofthe Denver type, the following compositions will be found forthe various products.
The density of PbS and SiO2 are 7.5 and 2.65 g/cc, respectively
PbS SiO2Feed, a 10 % 90 %
Concentration, b 80 20
Rougher tailings, c 2 98
Scavenger concentrate, d 11 89
Final tailings 0.5 99.5
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Determine:a. Density for all solids
b. Mass of products
c. Volume of tanks
d. Number of cells and power requirementusing Denver No. 24 which have 50 cu. ft
of volume
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Determine:E. Volume of delivered air and power
requirement of air compressor when Air-Lift
Machine by the Southwestern Engineering Co.is used (Assume 75 cfm air/ft in
Rougher, 60 cfm air/ft in scavenger, and 25
percent longer contact time at 2 psi).
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Air delivered, cfm Approximate Horsepower at Pressures of2 psi 3 psi 4 psi 5 psi
500 6 9.5 13.5 17.51000 12 18.5 26 332000 24 38 54 703000 34 57 76 964000 46 76 105 1355000 58 91 125 1606000 70 120 168 2207000 83 135 190 2458000 96 165 225 310
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Size, cubic ft Horsepower Consumed per CellDenver Fagergren
10 112 1.2 1.8-2.018 1.424 2.2 3.5-4.040 3.2 550 4.2 670 8100 9