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Evaluation of MicroEvaluation of Micro--bubble Flotation for Treatingbubble Flotation for Treating
UltraUltra--fine Particles andfine Particles and
Improvement by Applying Ultrasonic IrradiationImprovement by Applying Ultrasonic Irradiation
SDIMI 2013@Miros IslandSDIMI 2013@Miros IslandJuly 1July 1stst, 2013, 2013
S. OwadaS. Owada11, E. Matsunaga, E. Matsunaga22and N. Kurokiand N. Kuroki22
1 Faculty of Science and Engineering, Waseda University,1 Faculty of Science and Engineering, Waseda University,2 Graduate School of Creative Science and Engineering, Waseda Un2 Graduate School of Creative Science and Engineering, Waseda University,iversity,
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Further Treatment of Mineral ResourcesFurther Treatment of Mineral Resources
Lack of high grade ores Low grade and complex ore
treatment and/or Reuse of old (rich) tailings (Ultra-)
Fine grinding Fine (nano) particles treatment
Wastewater TreatmentWastewater TreatmentSolid/liquid separation and/or mutual separation of
precipitates to remove or recover specific components
Management of Hazardous ElementsManagement of Hazardous Elements
Hazardous elements are often concentrated into fine
(nano) fractions and necessary to be removed
BackgroundBackground
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Assumptions1. Homogeneity of particles
2. No interaction of particles3. No interaction of various flotation phenomena.
* Argument: Flotation follows 1st order kinetics.
* Weight floated dw in the time dt is proportional to the
product of residual particle weight and dw.
Flotation probabilityFlotation probability
Total Flotation Probability: Pflot =Pc *Pa * (1 -Pd)
Pc: Collision of particles and bubbles
Pa: Adhesion of particles to bubbles
(1 Pd
): Non-detachment of particles from bubbles
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20timesSectionalAreaand
Highercollision
probability
1
mm
50
m
Relationbetweenparticlesizeand
flotationprobability
ti: Induction time (s)
LOWLOW Collision
Probability
Necessity ofNecessity of MicroMicro--bubble Flotabubble Flotaionion
HIGHHIGH Collision
Probability
Particle size (m)
Particle size (m)
F
lotation
Pro
bability(-)
50 m
bubble
1 mm
bubbles
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Problems inProblems in MicroMicro--bubble Flotationbubble Flotation
1. Rising velocity is low because of small bubble size, then,
flotation capacity is low.
2. Although the effectiveness of micro-bubble flotation toimprove collision probability is clear butNOT adhesion and
non-detachment probabilities, and little experimental
validation.
3. Air-pressure and/or pulp-circulation types of micro-bubble
generators are difficult to control bubble size and flow rate.
Detailed theoretical and experimentalDetailed theoretical and experimental comparison ofcomparison of
MicroMicro-- and Milliand Milli--bubble flotationbubble flotation
Ultrasonic IrradiationUltrasonic Irradiation to air bubbles in order to solveto air bubbles in order to solvethe above problems and improve the effectivenessthe above problems and improve the effectiveness
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Detailed comparison ofDetailed comparison of
MicroMicro-- andand MilliMilli--Bubble FlotationBubble Flotation
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Pulp of hematite fines(0.45wt%
PD,220
mL)
10min
conditioning
pH
adjustmentwith
HNO3
orKOH
SDS
addition(1.0104 M)
33L
ofMIBC
Airbubbleintroduction
0.002
M withKNO3
Froth Tailin
g
10min
Flotation
Bubble size distributionat pH6, SDS 1.010-4 M
Micro-bubble
52m of 50% size
Milli-bubble
708m of 50% size
10m
-potential of hematitepH
potential(mV)
ExperimentalExperimental
pH
adjustmentwithHNO3
orKOH
Hematite finesSynthesized
by gel-sol method
pH 8.0 of IEP
Bubble sizeCumulativeun
dersize(wt%)
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Flotation results for Hematite finesFlotation results for Hematite fines
Micro-bubble
Milli-bubble
Micro-bubble
Milli-bubble
Flotationre
covery(%)
Flotationrateconstant(-)
Particle size (m) Particle size (m)
Relation between particle size and flotation recovery
/ flotation rate constant
It was confirmed that micro-bubble flotation has an advantage to milli-
bubble flotation in flotation recovery and the rate constant, especially in
finer size ranges.
It is also demonstrated that flotation recovery and the rate constantbecomes lower in finer size ranges with both flotation methods.
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Air
Particle
FluidStream
line
* Considering particle size and velocity* Considering particle size and velocity
dac PPPP -1=
Collision & DetachmentCollision & Detachment
ProbabilityProbability
Micro-bubble,
corrected
Milli-bubble,
corrected
Particle size (m)C
ollisionprobab
ility(-)
Micro-bubble
Milli-bubble
Particle size (m)Detachmentproba
bility(-)
Air
Particle
HeindelHeindel Collision Model,Collision Model, PPcc Drzymala Detachment Model,Drzymala Detachment Model, PPdd
Detachment force: Fde = Fw + Fd
Attachment force: Fat = Fc + Fe
Apparent gravity
of particleDrag of
particle
Vertical comp.
interface forceExcess force
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dac PPPP -1=
Yoon Adhesion ModelYoon Adhesion Model
Adhesion ProbabilityAdhesion Probability
Micro-bubble
Milli-bubble
Particle size (m)
Ad
hesionprobability(-)
Particle size (m)
Inductiontime
Inductiontime(m
s)
Micro-bubble
Milli-bubble
130
Re845exparctan2sin
pbb
ib
72.02
aRRR
tuPPPaa
Induction timeInduction time
Air
Particle
** Induction timeInduction time: must be shorterthan slipping timeslipping time for adhesion
AdhesionAdhesion
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Comparison ofComparison of MicroMicro--bubble Flotationbubble Flotation
withwith MilliMilli--bubble Flotationbubble Flotation
Micro-bubble
Milli-bubble
Milli-bubble
Micro-bubble
Micro-bubble
Milli-bubble
Non-detachmentprobability(-)
Particle size (m)
Collisionprobability(-)
Particle size (m)Particle size (m)
Micro-bubble
Milli-bubble
Flotationprobability(-)
Particle size (m)
Adhesionprob
ability(-)
Property of Micro-bubble flotation
compared with Milli-bubble flotation
Pc Pa P1-d
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Improvement of MicroImprovement of Micro--bubblebubbleFlotation by ApplyingFlotation by Applying
Ultrasonic IrradiationUltrasonic Irradiation
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Resonance
Strongvibration
Secondary Bjerknes force:
Interaction of bubbles
Secondary
ultrasonic vibration
is generated from
the bubbles
22222122010
22
22
L
RRAFB
1E38
1E36
1E34
1E32
1E
30
1E28
1E26
1E24
0 20 40 60 80 100
38kHz
430kHz F > 0: Attractive Coagulation andincorporation of bubbles
F < 0: Repulsive Dispersion of bubbles
AAmplitude of stationary wave
Frequency,R
10 &R
20
Bubble size,Liquid density
L
Distance between bubbles,
1 &2
Resonance frequency of
bubbles
Sec
ondaryBjerknesforce(N)
Bubble size (m)
Ultrasonic Irradiation to Air BubblesUltrasonic Irradiation to Air BubblesPrimary Bjerknes Force:
Change in bubble volumein the stationary wave
Neg.Press.
Pos.Press.
Neg.Press.
Size range of
micro-bubbles
in flotation
Anti-node
Node Anti-node
ResonantResonantBubble sizeBubble size
ResonantResonant
Bubble sizeBubble size
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Compre
sseda
ir
Ultrasoni
c
enerator
Air
SPGfilter
Flow meterImpellerrotator
Precisionregulator
Ultrasonicirradiator
High-speedCamera system
Lens
Lightsource
Flotation cell
Experimental of FlotationExperimental of Flotation
with Ultrasonic Irradiationwith Ultrasonic Irradiation
Impeller
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Measurement of bubble size distribution
by high-speed camera
Conditions:
SDS conc.: 1.0 * 10-3, 1.0 * 10-4, 1.0 * 10-5 M
MIBC: 150 L/LpH: 3.0, 7.0, 11.0
Ionic strength: 4.0 * 10-3 M
No. bubbles counted with high speed camera:
200 for single bubbles50 for coagulated bubbles
Bubbles
Observation area
430kHz 38kHz
Experimental of Bubbles ObservationExperimental of Bubbles Observation
Flotation cell
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0
20
40
60
80
100
10 100
430kHz
38kHz
Cumulativeundersize
(No.%
)
Coagulated bubblesCoagulated bubblesSingle bubblesSingle bubbles
Bubble size (m)
Coalescence of bubbles could lead to the higher selectivity of
mixed components.
Increase in bubble size could lead to the increase in flotationrate.
Bubble Size DistributionBubble Size Distribution
Non
Coales
cence
Bubble size (m)
0
20
40
60
80
100
10 100 1000
430kHz
38kHz
Non
Coagulation
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Feed
Tailing
Froth
Ultrasonic
irradiation
Micro-
bubble
generator
Plastics
Ultrasonic
irradiation
Tailing
Froth
Micro-
bubble
generator
Nobel MicroNobel Micro--bubble Flotation Systembubble Flotation System
For Higher capacity
& Higher selectivity
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Concentration of SDS [mol/L]
Flotatio
nrecovery
[%]
Dramatic decrease of apparent CMC with ultrasonic irradiation It might be suggested that the increase in hydrophobic interactionthe increase in hydrophobic interaction
among surfactant molecules can be achieved.
Non
Change in Flotation RecoveryChange in Flotation Recoverywith Ultrasonic Irradiationwith Ultrasonic Irradiation
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SDS
concentration of
50% flotation
Attractive force
between bubble-particle
Change in the SDS Concentration of 50% flotationChange in the SDS Concentration of 50% flotation
and Bubbleand Bubble--Particle Attractive ForceParticle Attractive Force
Flotation recovery can be achieved with much lower SDS
concentration in case of higher ultra-sonic frequency.
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ConclusionConclusion
1. Flotation recovery, rate constant, and the probability were higher in Micro-bubble flotation than in Milli-bubble flotation.
2. We modified Yoon flotation model and Heindel collision model byconsidering the bubbles and particles rising spaces and particle size.
3. Adhesion probability of particles to bubbles, which was obtained bycombining experimental flotation probability, Heindel model andDrzymala model, were lower in Micro-bubble flotation than in Milli-
bubble flotation.
4. Induction time, calculated from the adhesion probability, was increased bydecreasing particle size both in Micro- and Milli-bubble flotation, whichindicated that the energy to break bubble surface by particle attachmentwas smaller in the case of finer particles.
5. Bubbles were coalesced and/or coagulated by the secondary Bjerknessforce generated by ultrasonic irradiation. Ultrasonic wave whosefrequency is closer to the resonance frequency had a higher effect.
6. We demonstrated two kinds of Micro-bubble flotation systems with
ultrasonic irradiation in order to increase the capacity and selectivity.7. It might be suggested that ultrasonic irradiation of higher frequency
increased the flotation recovery with much lower collector concentration.
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Hydrophilicparticles
Hydrophobicparticles
Flotation
principle
Collision
Probability
dac PPPP -1=
CollisionAdhe
sion
aP
Non-
detatchment
Air
bubble
dP1
Collision
probability is
very low In
mm-size
bubbles
Difficulty inDifficulty in
fines flotationfines flotation
AirAirbubblesbubbles
Problem inProblem in MilliMilli--bubble Flotation:bubble Flotation:
Low CollisionLow Collision ProbabilityProbabilityHydrophobicparticles
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430kHz 9.63 38kHz 14.6
Decrease in Specific Surface AreaDecrease in Specific Surface Area
Flotation rate Grade Recovery
430kHz Fair Fair Fair
38kHz Excellent Excellent Low
Bubbles coalescence ratioBubbles coalescence ratio
Effect of Ultrasonic IrradiationEffect of Ultrasonic Irradiation
to Bubbles Behaviorto Bubbles Behavior
Effect of ultrasonic frequency to flotation behaviorEffect of ultrasonic frequency to flotation behavior