01_Evaluation of Microbubble Flotation for Treating Ultrafine Particles

8/10/2019 01_Evaluation of Microbubble Flotation for Treating Ultrafine Particles

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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.


21/23


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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

Documents

01_Evaluation of Microbubble Flotation for Treating Ultrafine Particles