Unlocking optimal flotation is the air recovery the key
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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?

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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

  • Modelling Flotation Froths

  • Useful froth equations


Froth flotation and froth physics

Froth Flotation and Froth Physics

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 motion

  • Liquid flow in the froth

  • Solids motion


Froth structure the physics of the froth

Froth Structure:The Physics of the Froth

Films between bubbles

Plateau borders


Froth motion from pulp to concentrate

Froth motion from pulp to concentrate

Laplace equation gives velocity

Boundary conditions:

  • Shape of tank and launders

  • Air entering the froth that overflows:

    AIR RECOVERY (%)


Unlocking optimal flotation is the air recovery the key

Froth Flow in Radial Equipment Designs


Liquid flow in the froth

Liquid Flow in the Froth

Three balanced forces act on the liquid in Plateau borders:

Gravity, capillary and viscous dissipation


Liquid motion and content

Liquid Motion and Content


Solids motion

Solids Motion

  • 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

Gangue Minerals

Mineral and Waste ParticlesExample of motion in Plateau borders


Mineral grade in froth

Mineral grade in froth


Unlocking optimal flotation is the air recovery the key

Froth Launder Design: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

Model validation


Tracking particles in flotation using pept1

Tracking particles in flotation using PEPT

Model validation


Simplified equations for flotation modelling

Simplified Equations for Flotation Modelling

Water flowrate to concentrate

Entrainment factor

Froth recovery

(α<0.5)


Water flowrate to concentrate

Water flowrate to concentrate


Entrainment factor ratio of gangue recovery to water recovery

ENTRAINMENT FACTOR Ratio of gangue recovery to water recovery


Froth recovery

Froth Recovery


Froth modelling summary

Froth Modelling Summary

  • 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

  • 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

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) at a specific air rate


Why is there a peak in air recovery par

Why is there a Peak in Air Recovery (PAR)?

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


Air recovery and flotation performance

Air Recovery and flotation performance

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


Froth appearance

Froth appearance

  • 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?

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

  • Measuring air recovery

  • Air rate effect and flotation performance

  • Bank air profiling using air recovery


Air rate profiling

Air rate profiling

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

  • 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

  • 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

  • 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

  • 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: Grade-Recovery and Air Recovery

76.3%

Cumulative recoveries:

75.6%


Study performed in two stages

Study performed in two stages

  • 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

  • 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


Air rate profiling performance

Air rate profiling: Performance


Air rate profiling findings

Air rate profiling: Findings

  • 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

  • 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: Preliminary tests


Air recovery optimisation air rate profiles

Air recovery optimisation: Air rate profiles


Air recovery optimisation air recovery

Air recovery optimisation: Air recovery


Air recovery optimisation performance

Air recovery optimisation: Performance


Air recovery optimisation performance of first cell

Air recovery optimisation: 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

  • 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


Unlocking optimal flotation is the air recovery the key

Summary and Conclusions

  • 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

  • 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?


Unlocking optimal flotation is the air recovery the key1

UNLOCKING OPTIMAL FLOTATION:is the AIR RECOVERY the key?

Jan Cilliers

Royal School of Mines

Imperial College London


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