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UNLOCKING OPTIMAL FLOTATION: is the AIR RECOVERY the key?. Jan Cilliers Royal School of Mines Imperial College London. Outline. The Origins of Air Recovery Modelling Flotation Froths Useful froth equations Air Recovery Application Measuring air recovery

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Unlocking optimal flotation is the air recovery the key

UNLOCKING OPTIMAL FLOTATION:is the AIR RECOVERY the key?

Jan Cilliers

Royal School of Mines

Imperial College London


Outline
Outline

The Origins of Air Recovery

  • Modelling Flotation Froths

  • Useful froth equations

    Air Recovery Application

  • Measuring air recovery

  • Air rate effect and flotation performance

  • Bank air profiling using air recovery


What is the air recovery

Air leaves a flotation cell by bursting on the top of the froth or overflowing into the concentrate.

The AIR RECOVERY is the fraction of the air that that overflows (and does not burst)

What is the Air Recovery?

Air leaving froth by bursting at top surface

Air overflowing the weir as froth

Froth concentrate

Air into the cell


The origins of air recovery
The Origins of Air Recovery froth or overflowing into the concentrate.

  • Modelling Flotation Froths

  • Useful froth equations


Froth flotation and froth physics
Froth Flotation and Froth Physics froth or overflowing into the concentrate.

The surface chemistry determines whether the minerals can be separated

The froth physics determines how well the separation happens

Requires a froth-phase model describing the physics


A flowing froth model components
A Flowing Froth Model - components froth or overflowing into the concentrate.

  • Froth motion

  • Liquid flow in the froth

  • Solids motion


Froth structure the physics of the froth
Froth Structure: froth or overflowing into the concentrate.The Physics of the Froth

Films between bubbles

Plateau borders


Froth motion from pulp to concentrate
Froth motion from pulp to concentrate froth or overflowing into the concentrate.

Laplace equation gives velocity

Boundary conditions:

  • Shape of tank and launders

  • Air entering the froth that overflows:

    AIR RECOVERY (%)


Froth Flow in Radial Equipment Designs froth or overflowing into the concentrate.


Liquid flow in the froth
Liquid Flow in the Froth froth or overflowing into the concentrate.

Three balanced forces act on the liquid in Plateau borders:

Gravity, capillary and viscous dissipation


Liquid motion and content
Liquid Motion and Content froth or overflowing into the concentrate.


Solids motion
Solids Motion froth or overflowing into the concentrate.

  • Attached Solids

    Particles attached to bubbles move with the froth

    Most particles are detached due to coalescence (>95%)

2. Unattached Solids:

Particles move in the Plateau borders

Follow the liquid, settle and disperse

Overflow into concentrate


Mineral and waste particles example of motion in plateau borders

Valuable Mineral froth or overflowing into the concentrate.

Gangue Minerals

Mineral and Waste ParticlesExample of motion in Plateau borders


Mineral grade in froth
Mineral grade in froth froth or overflowing into the concentrate.


Froth Launder Design: froth or overflowing into the concentrate.Effect of forcing froth to flow inwards or outwards

INTERNAL

CHANNEL

CHANNEL 1

CHANNEL 2

Internal Launder

Two Launders


Tracking particles in flotation using pept
Tracking particles in flotation using PEPT froth or overflowing into the concentrate.

Model validation


Tracking particles in flotation using pept1
Tracking particles in flotation using PEPT froth or overflowing into the concentrate.

Model validation


Simplified equations for flotation modelling
Simplified Equations for Flotation Modelling froth or overflowing into the concentrate.

Water flowrate to concentrate

Entrainment factor

Froth recovery

(α<0.5)


Water flowrate to concentrate
Water flowrate to concentrate froth or overflowing into the concentrate.


Entrainment factor ratio of gangue recovery to water recovery
ENTRAINMENT FACTOR froth or overflowing into the concentrate.Ratio of gangue recovery to water recovery


Froth recovery
Froth Recovery froth or overflowing into the concentrate.


Froth modelling summary
Froth Modelling Summary froth or overflowing into the concentrate.

  • Froth physics determines the effectiveness of the flotation separation

  • Complex froth zone simulators are available for operation and design

  • Simplified models have been developed for liquid recovery, froth recovery and entrainment, based on the physics

    All the froth models include

    THE AIR RECOVERY


Air recovery application
Air Recovery Application froth or overflowing into the concentrate.

  • Measuring air recovery

  • Air rate effect and flotation performance

  • Bank air profiling using air recovery


Air recovery a reminder

Air leaves a flotation cell by bursting on the top of the froth or overflowing into the concentrate.

The AIR RECOVERY is the fraction of the air that that overflows (and does not burst)

Air recovery.. a reminder

Air leaving froth by bursting at top surface

Air overflowing the weir as froth

Froth concentrate

Air into the cell


Measuring the air recovery
Measuring the air recovery froth or overflowing into the concentrate.

Air leaving through bursting

Air Recovery =

Volumetric flowrate air overflowing

Air flowrate into cell

Volumetric flowrate air overflowing

= overflowing velocity x overflowing froth height x lip length

Overflowing froth height

Overflowing velocity

Air flowing over lip

Air In


Air recovery shows a maximum par at a specific air rate
Air Recovery shows a maximum (PAR) froth or overflowing into the concentrate.at a specific air rate


Why is there a peak in air recovery par
Why is there a Peak in Air Recovery (PAR)? froth or overflowing into the concentrate.

Optimum balance between froth stability and motion

Air

Recovery

Bubbles heavily loaded

Stable, but move slowly

Bubbles under-loaded

Unstable, burst quickly

Air Velocity into Flotation Cell


Predicting air recovery theory
Predicting air recovery – theory froth or overflowing into the concentrate.


Air recovery and flotation performance
Air Recovery and flotation performance froth or overflowing into the concentrate.

Air rate that gives highest air recovery also gives highest mineral recovery


Froth appearance
Froth appearance froth or overflowing into the concentrate.

  • Air rate 8m3 min-1

  • Air recovery 70%

  • Air rate 12m3 min-1

  • Air recovery 40%


Why does the air recovery affect flotation
Why does the Air Recovery affect flotation? froth or overflowing into the concentrate.

Optimum balance between froth stability and motion

High recovery and grade

Metallurgical

Recovery

Air

Recovery

INCREASE AIR

Reduce grade

Increase recovery

REDUCE AIR

Increase grade

Increase recovery

Bubbles heavily loaded

Stable, but move slowly

Bubbles under-loaded

Unstable, burst quickly

Air Velocity into Flotation Cell


Air recovery application1
Air Recovery Application froth or overflowing into the concentrate.

  • Measuring air recovery

  • Air rate effect and flotation performance

  • Bank air profiling using air recovery


Air rate profiling
Air rate profiling froth or overflowing into the concentrate.

The air rate profile in a flotation bank affects the performance

  • Two strategies:

    • Determine the best air rate profile

      • Vary distribution of a set total air addition

    • Determine the optimal total air addition

      • Vary the total air addition with a set air profile


Air rate profiling approaches
Air rate profiling approaches froth or overflowing into the concentrate.

  • Different air profiles with same total addition

  • (e.g. Cooper et al., 2004)

2. Different air addition with the same profile

(Hadler et al., 2006)


Air profiling strategies
Air Profiling Strategies froth or overflowing into the concentrate.

  • Determine the best air rate profile

    • Vary distribution of the total air addition

    • Increasing profile typically improves performance

      e.g. Cooper et al., 2004; Gorain, 2005; Hernandez-Aguilar and Reddick, 2007; Smith et al., 2008

  • Determine the optimal total air addition


Determining the air rate profile
Determining the air rate profile froth or overflowing into the concentrate.

  • Increasing profile typically yields better performance

    Higher cumulative grade for same cumulative recovery

    (e.g. Cooper et al., 2004)


Introduction previous work
Introduction: Previous work froth or overflowing into the concentrate.

  • Determine the best air rate profile

  • Determine the optimal total air addition

    • Best performance at air rate giving

      Peak Air Recovery (PAR)

      e.g. Hadler et al., 2006; Hadler and Cilliers, 2009


Cu rougher performance grade recovery and air recovery
Cu Rougher Performance: froth or overflowing into the concentrate.Grade-Recovery and Air Recovery

76.3%

Cumulative recoveries:

75.6%


Study performed in two stages
Study performed in two stages froth or overflowing into the concentrate.

  • Air rate profiling tests

  • Air recovery optimisation (PAR) tests

    First direct comparison of the two approaches


Stage 1 air rate profiles
Stage 1: Air rate profiles froth or overflowing into the concentrate.

  • Air rate profiling tests

    • Three profiles tested, the ‘Standard’ and two others, all adding same total air

  • Air recovery optimisation


Air rate profiling air rate profiles
Air rate profiling: Air rate profiles froth or overflowing into the concentrate.


Air rate profiling performance
Air rate profiling: Performance froth or overflowing into the concentrate.


Air rate profiling findings
Air rate profiling: Findings froth or overflowing into the concentrate.

  • Order of cumulative Cu recovery is same as cumulative air recovery

    • Sawtooth > Stepped > Standard

      Mineral recovery and air recovery qualitatively linked


Stage 2 peak air recovery test
Stage 2: Peak Air Recovery test froth or overflowing into the concentrate.

  • Air rate profiling test

  • Air recovery optimisation

  • Preliminary tests to find PAR air rates

  • Test conducted at PAR air rates

  • Total air added same as ‘Standard’ profile


Air recovery optimisation preliminary tests
Air recovery optimisation: froth or overflowing into the concentrate.Preliminary tests


Air recovery optimisation air rate profiles
Air recovery optimisation: froth or overflowing into the concentrate.Air rate profiles


Air recovery optimisation air recovery
Air recovery optimisation: Air recovery froth or overflowing into the concentrate.


Air recovery optimisation performance
Air recovery optimisation: Performance froth or overflowing into the concentrate.


Air recovery optimisation performance of first cell
Air recovery optimisation: froth or overflowing into the concentrate.Performance of first cell

  • Effect of air rate:

    • Recovery maximum at PAR air rate

    • Upgrade ratio decreases with increasing air rate


Air profiling using air recovery summary
Air profiling using air recovery: Summary froth or overflowing into the concentrate.

  • Air profiling can significantly improve flotation performance

  • The performance improvement is a froth effect; rate kinetics alone cannot explain it

  • The air rate giving the highest air recovery (PAR) also gives the best flotation

  • The PAR method simultaneously determines the optimal bank air rate and distribution


Summary and Conclusions froth or overflowing into the concentrate.

  • Froth physics determines the effectiveness of flotation

  • Froth models indicate important variables – this is the origin of AIR RECOVERY

  • Air recovery is affected by air rate; there is an air rate at which the air recovery is a maximum (PAR)

  • The Peak Air Recovery (PAR) methodology simultaneously establishes the correct air addition rate and the best air rate profile for a flotation bank

  • Significant improvements observed; plant control strategy


Acknowledgements
Acknowledgements froth or overflowing into the concentrate.

  • Rio Tinto Centre for Advanced Mineral Recovery at Imperial College London

  • Froth and Foam Research team

  • Intellectual Property Rights

  • The peak air recovery-based froth flotation optimisation methodology is protected by a PCT-stage patent application, covering most of the countries of the world, with additional protection in Chile and Peru


Questions
Questions? froth or overflowing into the concentrate.


Unlocking optimal flotation is the air recovery the key1

UNLOCKING OPTIMAL FLOTATION: froth or overflowing into the concentrate.is the AIR RECOVERY the key?

Jan Cilliers

Royal School of Mines

Imperial College London


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